Method for separating liquids

ABSTRACT

METHOD AND APPARATUS FOR REMOVING A LAYER OF A FIRST LIQUID FROM A BODY OF A SECOND LIQUID. SAID FIRST LIQUID IS CAUSED TO SELECTIVELY FLOW THROUGH THE PORES OF AND INTO A POROUS COLLECTON CUP IMMERSED THEREIN, APPLICA-   TION OF AN ELECTRIC CURRENT TO SAID CUP INCREASES THE SELECTIVITY THEREOF FOR SAID FIRST LIQUID.

March 19, 1974 w. v. CHILDS METHOD FOR SEPARATING LIQUIDS Original Filed Sept. 17. 1969 INVENTOR. W.V. CHILDS amp 2 5 O N 5 m V T 8 M 4 m 6 S 4 8 3 T 2 3 4 m M x D 4 A m 5 o P VAT L I 4 5 r 4 m W. j III: E 6 D 6 3 05+ I M v E d TAB w 4 v? v M M a 0 W5 9 w A AU 2 n a a TCB & f F 2 i lilfill (18 O 2 6 M W 2 4 M W 1 m lllllllll ll hrrok/vsrs 3,798,144 METHOD FOR SEPARATING LIQUIDS William V. Childs, Bartlesville, Okla., assiguor to Phillips Petroleum Company Original application Sept. 17, 1969, Ser. No. 858,734, new Patent No. 3,617,453. Divided and this application May 17, 1971, Ser. No. 143,892

Int. Cl. B01d 13/02; B03c 5/00 US. Cl. 204-186 6 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for removing a layer of a first liquid from a body of a second liquid. Said first liquid is caused to selectively flow through the pores of and into a porous collection cup immersed therein. Application of an electric current to said cup increases the selectivity thereof for said first liquid.

This application is a division of my copending application Ser. No. 858,734, filed Sept. 17, 1969, now US. Pat. No. 3,617,453, issued Nov. 2, 1971.

This invention relates to an electrochemical conversion process.

Electrochemical conversion processes for converting a wide variety of feedstocks to desirable products are well known in the art. These processes include processes described an anode processes, e.g., processes wherein the desired reaction is carried out at or in the region of the anode, and also processes described as cathode processes, e.g., processes wherein the desired reaction is carried out at or in the region of the cathode. In many electrochemical conversion processes it is often desirable to maintain the electrolyte temperature at a desired value or at least within a narrow range of temperature. This sometimes becomes quite diflicult due to PR losses within the electrolyte, coupled with the unavoidable heat of reaction. It is known to cool electrolytic cells by circulating various coolants in coils or tubes disposed within the cell. However, the most convenient coolant, water, frequently reacts with the electrolyte when leakage of the coolant occurs. In many cells there is also the danger of contaminating the products of the process with the coolant or with products of the reaction between the coolant and the electrolyte. Leakage of cooling water into the electrolyte is not an uncommon occurrence in view of the thinwalled cooling tubes employed and the corrosiveness of some cooling waters and some electrolytes.

The invention now being claimed in said copending application provides an electrochemical conversion process comprising a novel method of feeding a porous electrode and wherein a solution is provided for the problem of maintaining the cell temperature within desired limits. Broadly speaking, in the practice of said invention a liquid layer comprising the feedstock to the cell is maintained on the surface of the electrolyte in said cell. A portion of said liquid layer passes into the pores of a porous electrode in the cell and within said pores is at least partially converted. A vaporous cell efiluent stream comprising converted products and unconverted feedstock is withdrawn through a reflux condenser. Condensate from said condenser is returned to the cell to cool the electrolyte therein. Conversion products are recovered from the noncondensed portion of said cell efliuent stream. In one presently preferred embodiment, a portion of the feedstock is also introduced into the bottom portion of said porous electrode.

According to the invention being claimed in this application, there is provided a method of removing a layer of a second liquid from a body of a first liquid, said liquids being substantially insoluble in each other, which method comprises: causing said second liquid to selec- United States Patent 0 tively flow through the pores of and into a porous collection cup immersed therein; and then flowing said second liquid from said cup through a conduit connected thereto.

Further according to the invention being claimed in this application, there is provided apparatus comprising, in combination: a vessel for containing a body of a first liquid having a body of a second liquid, essentially insoluble in said first liquid, disposed as a layer on the surface of said first liquid; a phase splitter means disposed in said container, extending through said layer of second liquid and into said first liquid, for selectively removing said second liquid from the surface of said first liquid; and means for causing said second liquid to selectively flow into said phase splitter means and be removed from said cell.

The invention is particularly applicable to electrochemical conversion processes in which porous electrodes can be employed. Some examples of such processes are electrochemical halogenation, electrochemical cyanation, and cathodic conversions such as the reduction of alcohols to hydrocarbons, the reduction of organic ozonolysis products, or the reduction of organic acids to alcohols. One electrochemical conversion process in which the invention is particularly valuable is the electrochemical fluorination of fiuorinatable materials in the presence of an essentially anhydrous liquid hydrogen fluoride-containing electrolyte. Thus, for purposes of convenience, and not by way of limitation, the invention will be further described in terms of being employed in the electrochemical fluorination of fiuorinatable materials when using said hydrogen fluoride-containing electrolyte.

Various processes for carrying out electrochemical fluorination reactions are known. In one presently preferred process a current-conducting, essentially anhydrous, liquid hydrogen fluoride electrolyte is electrolyzed in an electrolysis cell provided with a cathode and a porous anode (preferably porous carbon), a fiuorinatable feedstock is introduced into the pores of said anode and at least a portion of said feedstock is at least partially fluorinated within the pores of said anode, and fluorinated products are recovered from the cell.

Very few organic compounds are resistant to fluorination. Consequently, a wide variety of feed materials, both normally liquid and normally gaseous compounds, can be used as feedstocks in said process. Generally speaking. desirable organic starting materials which can be used are those containing from 2 to 12, preferably 2 to 10, carbon atoms per molecule. Some general types of organic starting materials which can be used include, among others, the following: alkanes, alkenes, alkynes, amines, ethers, esters, mercaptans, nitriles, alcohols, aromatic compounds, and partially halogenated compounds of both the aliphatic and aromatic series. It will be understood that the above-named types of compounds can be either straight chain, branched chain, or cyclic compounds.

The hydrogen fluoride electrolyte can contain small amounts of Water, such as up to about 5 weight percent. However, it is preferred that said electrolyte be essentially anhydrous, e.g., contain not more than about 0.1 weight percent water. Commercial anhydrous liquid hydrogen fluoride containing up to about 1 percent by weight of water can be used. Thus, as used herein and in the claims, unless otherwise specified, the term essentially anhydrous liquid hydrogen fluoride includes liquid hydrogen fluoride which can contain water not exceeding up to about 1 percent by weight. As the electrolysis reaction proceeds, any water contained in the hydrogen fluoride electrolyte is slowly decomposed and said electrolyte concomitantly approaches the anhydrous state. Pure anhydrous liquidhydrogen fluoride is nonconductive. To provide adequate conductivity in the electrolyte, and to reduce the hydrogen fluoride vapor pressure at cell operating conditions, an inorganic additive can be incorporated in the electrolyte. Presently preferred additives for this purpose are the alkali metal fluorides and ammonium fluoride. Said additives can be utilized in any suitable molar ratio of additive to hydrogen fluoride within the range of from 1:4.5 to 1:1, preferably 1:4 to 1:2.

Generally speaking, the fluorination process can be carried out at temperatures within the range of from -80 to 500 C. at which the vapor pressure of the electrolyte is not excessive, e.g., less than 250 mm. Hg. It is preferred to operate at temperatures such that the vapor pressure of the electrolyte is less than about 50 mm. Hg. A presently preferred range of temperature is from about 60 to about 120 C.

Pressures substantially above or below atmospheric can be employed if desired, depending upon the vapor pressure of the electrolyte and the vapor pressure of the feedstock as discussed above. Generally speaking, the process is conveniently carried out at substantially atmospheric pressure.

Current densities within the range of 30 to 1000, or more, preferably 50 to 500, milliamps per square centimeter of anode geometric surface can be used. The voltage which is normally employed will vary depending upon the particular cell configuration employed and the current density desired. Under normal operating conditions, however, the cell voltage or potential will be less than that required to evolve or generate free or elemental fluorine. Voltages in the range of 4 to 12 volts are typical. Generally speaking, the maximum normal voltage will not exceed 20 volts per unit cell. The term anode geometric surface refers to the outer geometric surface area of the porous element of the anode which is exposed to the electrolyte and does not include the pore surfaces of said porous element.

Feed rates which can be employed will preferably be within the range of from 0.5 to ml. per minute per square centimeter of anode geometric surface area. For convenience, the volumetric feed rates have been expressed in terms of gaseous volume calculated at standard conditions, even though the feedstock may be introduced into the porous anode in liquid state.

Further details regarding fluorinatable feedstocks, feed rates, and other information concerning said preferred electrochemical fluorination process can be found in said copending application Ser. No. 858,734, filed Sept. 17, 1969, now U.S. Pat. 3,617,453, issued Nov. 2, 1971.

Referring now to the drawing, the invention will be more fully explained. In the drawing there is illustrated an electrolytic cell, denoted generally by the reference numeral 10, comprising a cell body 11 having an anode 12 disposed therein. As here illustrated, said anode comprises a cylinder of porous carbon. Preferably, said anode is vertically disposed as illustrated. A current collector 14, formed of copper or other suitable conducting material, is provided in intimate contact with the interior of said porous carbon cylinder. The intimate contact between said current collector and said cylinder of porous carbon can be provided by threads, a tight wedge fit, or other suitable means. As illustrated, said current collector comprises a tubular conduit having a passageway 29 therein and extending into said cylinder of porous carbon to a point near the bottom thereof. Said current collector is connected by means of lead 16 to the anode bus of the current supply. It will be noted that the upper end portion of said anode 12 extends above the electrolyte level 18. A circular cathode 20, which can be a screen formed of a suitable metal such as a stainless steel, surrounds said anode 12 and is connected to the cathode bus of the current supply by a suitable lead wire 22. Any suitable source of current and connections thereto can be employed in the practice of the invention. Thermocouple means 23 is provided for determining the temperature of the electrolyte. A feedstock inlet 24 is provided in the upper portion, preferably the top, of said cell. A feedstock conduit 26 is type of valve. As here illustrated, said 'valve comprises a motor valve. A liquid level control means 30 is mounted on the wall of said cell body 11 and is operatively connected in conventional manner to said valve 28 for controlling the introduction of feedstock into the cell responsive to said liquid level controller 30. Any suitable type of liquid level controller can be employed. One suitable type is a Dynatrol detector type CL-lO-RH manufactured by the Automation Products, Inc., Houston, Tex. A reflux condenser means 32 is operatively connected to the upper portion of said cell body 11, preferably the top, and is in communication with the vapor space within said cell. Conduits 34 and 36 are provided for the supply of a suitable coolant to said reflux condenser 32.

A phase splitter means comprising a tubular conduit 38 having a passageway 41 therein, formed of a suitable metal or other conducting material, and a porous cup 40 mounted on and closing the lower end of said tubular conduit, is disposed in said cell body 11. Preferably, said cup 40 is mounted on said tubular conduit 38 in such a manner as to leave an enclosed space at the lower end of said tubular conduit. Preferably, said tubular conduit 38 of the phase splitter extends through the top or lid of the cell body 11. However, if desired, it is within the scope of the invention for said tubular conduit 38 to be curved and extend through a side wall of cell body 11. Said tubular conduit 38 is connected by means of a suitable lead Wire 42 to the anode bus of the current supply. A withdrawal conduit 44 is connected to the passageway 41 formed within said tubular conduit 38. Conduit 46, connected to said withdrawal conduit 44, extends into trap 48 as illustrated. Conduit 50, having vacuum pump means 52 disposed therein, is connected to the top of said trap 48. Returning to said anode, a conduit 27 is connected to the passageway 29 formed within the tubular current collector 14. Said conduit 27 is also connected at its other end to feedstock header conduit 25. An inlet 54 is connected to the top of cell body 11 for introducing gas pressure into the vapor space within said cell body.

In the operation of the apparatus illustrated in the drawing, for example, for the electrochemical fluorination of ethylene dichloride (1,2-dichloroethane) having a boiling point of about 83.5 C. and when using a KF'ZHF electrolyte, the temperature of said electrolyte can be maintained at about C. and the temperature of the anode can be maintained at about C. The temperature of the electrolyte can be controlled by the amount of reflux returned to the cell from reflux condenser 32. In some instances, it is desirable to maintain the temperature of the electrolyte slightly below, e.g., within the range of about 2 to about 60, preferably about 3 to about 20", below the boiling point of the liquid layer maintained on top of the electrolyte. However, in other instances, it will be desirable to maintain the temperature of the electrolyte essentially at the boiling point of said liquid layer. The temperature of'the anode can be controlled by controlling the amount of reaction taking place within the pores of said anode. This can be accomplished by balancing or correlating the feed flow rate and the current density applied to the anode. For a given feed flow rate to the anode, an increase in current density will result in a higher temperature within the pores of the anode, and vice versa. Generally speaking, it is desirable to maintain the temperature within the pores of the anode within the range of about 5 to about 20, preferably about 7 to about 15 C., above the electrolyte temperature. The temperature within the pores of anode 12 can be deter-mined by means of thermocouple(s) 29 embedded therein.

In one embodiment, the fresh feedstock is introduced to the cell exclusively through feed inlet 24 and a layer of feedstock is established on the surface of the electrolyte. The depth of said layer will depend upon the particular feedstock, the type of reaction being carried out, the size of the cell, the size and number of anodes in the cell, etc. Generally speaking, it will be desirable to maintain the depth of said layer within the range of about 0.1 to 2 inches, preferably about 0.5 to 1 inch. After the layer of feedstock has been established on the surface of the electrolyte, the current is turned on. The feedstock enters into the pores of the anode wherein it diffuses through the pores of the anode, is vaporized, contacts the fluorinating species, and at least a portion of said feedstock is at least partially fluorinated. Fluorinated product and any unfluorinated feedstock are passed from the pores of the anode above the level of the electrolyte and the supernatant layer thereon and into the vapor space in the upper portion of the cell. A vaporous cell eflluent stream is withdrawn through reflux condenser 32. Said condenser is operated at a temperature and a pressure such that hydrogen fluoride and at least a portion of the unfluorinated feedstock will be condensed. The non-condensed portion of said vaporous cell eflluent stream is passed through conduit 35 to a product separation zone wherein separation of the fluorinated products is effected in conventional manner.

In another preferred embodiment, the feeding of the anode from the supernatant layer of feedstock is supplemented by introducing fresh feedstock into the lower portion of the anode. In this embodiment, at least a portion of the fresh feedstock is introduced via conduit 27 and passed through passageway 29 into space 31 in the lower portion of the anode. In this embodiment, it is sometimes preferred to introduce all the fresh feedstock via space 31. From said space 31 the vaporized feedstock enters the pores of the anode, travels upward through the pores of the anode, and exits from the anode above the level of the electrolyte and supernatant liquid layer thereon, and into the vapor space in the upper portion of the cell. During passage of said feedstock through said pores at least a portion of the feedstock is at least partially fluorinated. A vaporous cell efiiuent stream is withdrawn through reflux condenser 32 and treated in the manner described above. When operating with this dual feeding system, the ratio of the feed introduced through space 31 to the feed introduced into the pores of the anode from layer 19 will usually be within the range of 0.5 to 0.95, preferably within the range of from 0.5 to 0.75. An important advantage of said dual feeding system is that if the feed to the lower portion of the anode is inadvertently interrupted, the supernatant layer on the surface of the electrolyte comprises a reservoir of feedstock. This will prevent, or at least reduce, production of elemental fluorine such as would occur if feedstock flow were suddenly stopped.

In practice, there will sometimes be a buildup of concentration of higher boiling fluorinated products in layer 19 which is maintained on the surface of the electrolyte. When the concentration of said higher boiling fluorinated products in layer 19 reaches a desired or limiting value, e.g., about 50 percent, it is desirable to remove a portion of said layer. I have discovered that this can be accomplished etficiently by utilizing the difference in contact angle of the electrolyte and the contact angle of the liquid in layer 19.

For example, the electrolyte KF-ZI-[F does not wet porous carbon, i.e., the contact angle of said electrolyte with the porous carbon is greater than 90 degrees. Thus, the electrolyte KF-2HF resists flow into the pores of the porous carbon. The contact angle of 1,2-dichloroethane and its fluorinated products is less than the contact angle for said electrolyte. These materials will thus preferentially or selectively flow into and through the pores of the porous carbon cup 40.

Referring to the drawing, this preferential or selective flow of layer 19 into and through the pores of porous cup 40 into collection zone 43 can be caused to take place by the application of gas pressure through inlet 54. Any suitable inert gas, such as nitrogen, can be employed for applying gas pressure. The application of said gas pressure will cause the layer 19 to flow through the pores of porous cup 40 and pass upwardly through passageway 41 and into conduit 44 for disposal as desired. When all of the liquid in layer 19 has been forced out, the gas pressure will purge the system and leave the electrolyte behind essentially undisturbed. Said layer 19 can also be caused to flow through the pores of porous cup 40 by the application of vacuum. Said vacuum can be applied to trap 48 by means of pump 52 disposed in conduit 50 connected to the top of trap 48. Thus, by opening the valve in conduit 46 and closing the valve in conduit 44, layer 19 can be caused to flow through the pores of cup 40, up through passageway 41, and into tray 48.

I have also discovered that the efiiciency of the above method of separating layer 19 from the underlying layer of electrolyte can be increased by applying a positive voltage to the phase splitter device. Said voltage can be applied by connecting lead wire 42 to the anode bus of the system. Current flow will be established because cup 40 extends into the electrolyte which is in contact with cathode 20. It will generally be desirable to apply from 3 to 8 volts of direct current to the phase splitter at a current density level within the range of from about 1 to about 300 milliamps per square centimeter of geometric surface area.

The above-described method of separating two phases can be applied to any system in which the contact angle of one phase (either phase) is greater than degrees, and the contact angle of the other phase is sufliciently different from, preferably less than, the contact angle of the firstmentioned phase. Generally speaking, it is desirable that the difference in said contact angles be at least 10 degrees. However, by the application of electric current as described above, the difference in contact angle can be increased and the initial difference in contact angle of the two phases is not unduly restrictive. While said phase splitter and its operation have been described as employing porous carbon for the porous cup 40, the invention is not limited to the use of porous carbon. Other suitable porous materials, such as porous Teflon, can be employed in the practice of the invention.

While certain embodiments of the invention have been described for illustrative purposes, the invention is not limited thereto. Various other modifications of the invention will be apparent to those skilled in the art in view of this disclosure. Such modifications are within the spirit and scope of the disclosure.

I claim:

1. A method of separating a layer of a second liquid from a layer of a first liquid, said liquids being substantially insoluble in each other, which method comprises:

causing one of said liquids to selectively flow through the pores of and into an electrically conductive p0- rous collection cup which is in contact with both of said liquids; and

applying a positive electric voltage to said cup so as to increase the selectivity of said cup for the flow of said one liquid through the pores of said cup.

2. A method according to claim 1 wherein: said second liquid comprises a fluorinatable organic material; said first liquid comprises a current-conducting, essentially anhydrous, hydrogen fluoride electrolyte; and said collec tion cup is formed of porous carbon.

3. A method according to claim 2 wherein: said voltage is within the range of from about 3 to about 8 volts and is applied to said collection cup at a current density within the range of from about 1 to about 300 milliamps per square centimeter of geometric surface area of said cup.

4. A method according to claim 1 wherein:

said liquids are disposed in a container;

. said porous cup and a conduit connected thereto define an enclosed space within said container which is not in communication with said liquids except through the pores of said cup; and said one liquid is caused to selectively flow into said cup by (a) the application of gas pressure to the surface of one of said liquids, or (b) the application of vacuum to a conduit connected to said cup. 5. A method according to claim 4 wherein: said second liquid comprises a fluorinatable organic material; and said first liquid comprises a current-conducting, essentially anhydrous, hydrogen fluoride electrolyte. 6. A method according to claim 5 wherein: said voltage is within the range of from about 3 to about 8 volts and is applied to said collection cup at a current density within the range of from about 1 to about 300 milliamps per square centimeter of geometric surface area of said cup.

References Cited UNITED STATES PATENTS THOMAS TUFARIELLO, Primary Examiner US. Cl. X.R. 

